Version: Blender 4.2 LTS and +

Content:

three geometry nodes setups for laying solar panels:

Flat terrain (no raycast)

relief terrain (raycast on terrain)

Roof (variation of flat terrain)

How to use it:

See scene examples.  Instances and geometry are set for 10x10 meters squares.

Note:

If you have a slow computer, depending on the size of the solar field, you might avoid enabling instances on screen and keep them for render only.